Many modern aircraft, as well as other vehicles and industrial processes, employ gas turbine engines for generating energy and propulsion. Such engines include a compressor, combustor and turbine, and in some cases a fan, provided in serial fashion, forming an engine core and arranged along a central longitudinal axis. Air enters the gas turbine engine through the front end and is pressurized in the compressor. This pressurized air is mixed with fuel in the combustor. The fuel-air mixture is then ignited, generating hot combustion gases that flow downstream to the turbine. The turbine is driven by the exhaust gases and mechanically powers the compressor and fan via a central rotating shaft. Energy from the combustion gases not used by the turbine is discharged through an exhaust nozzle, producing thrust to power the aircraft.
Gas turbine engines contain an engine core and fan surrounded by a fan case, forming part of a nacelle. The nacelle is a housing that contains the engine. The fan is positioned forward of the engine core and within the fan case. The engine core is surrounded by an engine core cowl and the area between the nacelle and the engine core cowl is functionally defined as a fan duct. The fan duct is substantially annular in shape to accommodate the airflow from the fan and around the engine core cowl. The airflow through the fan duct, known as bypass air, travels the length of the fan duct and exits at the aft end of the fan duct at an exhaust nozzle.
In addition to thrust generated by combustion gasses, the fan of gas turbine engines also produces thrust by accelerating and discharging ambient air through the exhaust nozzle. Various parts of the gas turbine engine generate heat while operating, including the compressor, combustor, turbine, central rotating shaft and fan. To maintain proper operational temperatures, excess heat is often removed from the engine via oil coolant loops, including air/oil or fuel/oil heat exchangers, and dumped into the bypass airflow for removal from the system.
In operation, the gas turbine engine may encounter a variety of weather conditions, including fog, ground freezing fog, hail, icing and rain. All of such inclement weather conditions can adversely affect engine operation. Currently, gas turbine engines have a limited ability to modify their operation to best address such conditions.
Accordingly, there is a need for an improved variable-geometry system for a gas turbine engine better able to operate under inclement weather conditions.